Volumetric umbilical artery blood flow: comparison of the normal versus the single umbilical artery cord

Single Umbilical Artery Umbilical Cord Is Associated With High-Grade Distal Fetal Vascular Malperfusion

PURPOSE AND CONTEXT

Umbilical cord abnormalities with clinical signs of cord compromise are frequently associated with fetal vascular malperfusion (FVM). Single umbilical artery (SUA) has been reported to be associated with high-grade FVM in fetal growth restriction but not in an unselected population; our study aimed to address this issue.

METHODS

Clinical and placental phenotypes of 55 consecutive placentas with SUA (Group 1) were compared with those of 655 placentas with 3-vessel umbilical cord (Group 2) from patients who were in the second half of their pregnancy. The placentas were histologically examined using hematoxylin and eosin (H&E) staining and CD 34 immunostaining.

KEY RESULTS

Several umbilical cord phenotypes and high-grade distal FVM, based on H&E staining and endothelial fragmentation by CD34 were significantly more common in Group 1, whereas decidual clusters of multinucleate trophoblasts were more common in Group 2. Notably, H&E staining or CD34 immunostaining evaluated separately showed that high-grade distal FVM was more common in Group 1 than in Group 2, but the difference was not statistically significant.

CONCLUSIONS

SUA predisposes to remote, advanced, and recent high-grade distal villous FVM, with a pathogenesis partly different from that of stasis-induced FVM, likely related to fetal anomalies associated with SUA.

Normal umbilical artery doppler values in 18-22 week old fetuses with single umbilical artery

Umbilical cord with a single umbilical artery (SUA) can carry twice the blood volume of a three-vessel cord (TVC). So, the normal hemodynamics of the fetuses with SUA was different from those with TVC. Furthermore, structural abnormalities, fetal aneuploidy, and intrinsic growth retardation may be associated with the presence of a SUA. In order to evaluate these patients, intermittent doppler measurements have been suggested. From this point, we aimed to determine the CDUS flow parameters in SUA cases and to demonstrate that these flow parameters are different from the TVC parameters. Ultrasound (US) examinations were performed in the 18-22 weeks of gestation during routine fetal anatomy screening. Resistance index (RI), Pulsatility index (PI), and S/D: systole to diastole ratio values were measured. The samples were taken from the proximal, mid-portion, and distal of the umbilical cord. In addition to Doppler Ultrasound values, AC and estimated fetal weight (EFW) values were also recorded. The study included 167 pregnant women, 86 of whom were study group with SUA and 81 were control group with TVC. The measurements of RI, PI, and S/D at all three levels were significantly lower in the SUA group compared to the TVC group. The resistance in the UA of fetuses with SUA is lower than in fetuses with TVC. The resistance in the UA of fetuses with SUA decreases from the fetal end to the placental end. Knowing the normal values for fetuses with SUA might provide a better and more reliable Doppler Ultrasoundassessment.

Impact of fetal trisomy 21 on umbilical artery Doppler indices

OBJECTIVES

Umbilical artery (UA) Doppler indices are surrogate measures of placental function, most commonly used to assess fetal wellbeing in pregnancies with fetal growth restriction. Fetuses with trisomy 21 (t21) are reported to have elevated UA Doppler indices, but reference percentiles are currently lacking for this population. We hypothesized that gestational age-specific values of UA Doppler indices in pregnancies complicated by t21 will be elevated compared to established percentiles based on euploid pregnancies. We aimed to assess UA Doppler indices longitudinally in fetuses with t21 in order to demonstrate Doppler patterns across gestation in this population, compare them with euploid fetuses, and investigate their association with pregnancy outcomes.

METHODS

We conducted a retrospective cohort study of singleton pregnancies with confirmed fetal t21 who underwent UA Doppler surveillance antenatally from January 2012 to August 2019. UA Doppler indices, including systolic/diastolic (S/D) ratio, pulsatility index (PI), and resistance index (RI) were extracted from ultrasound reports or directly from ultrasound images. UA S/D, PI, and RI percentiles by gestational week were created from available observations from our cohort via a data-driven approach using a generalized additive model. A secondary analysis was run to statistically compare t21 values to established percentiles based on observations from a historical population of euploid fetuses.

RESULTS

UA Doppler measurements from 86 t21 fetuses and 130 euploid fetuses were included in our analysis. Median (IQR) maternal age in t21 pregnancies and euploid pregnancies were 35 years (29-38) and 30 years (27-33), respectively. As in euploid fetuses, we found a negative association between Doppler indices and gestational age in the t21 fetuses. Maternal tobacco use, obesity, or chronic hypertension had no significant effect on UA Doppler indices. As hypothesized, values for UA S/D ratio, PI, and RI at the 2.5th, 5th, 10th, 25th, 50th, 75th, 90th, 95th, and 97.5th percentiles by gestational week were significantly higher in t21 fetuses compared to euploid fetuses (p<.001). Overall, 55.8% (48/86) of the t21 fetuses demonstrated at least one Doppler value above the 95th percentile for gestational age based on euploid reference standard. At birth, eight (9.3%) of the t21 fetuses were small for gestational age. When these pregnancies were removed from analysis, UA Doppler indices remained significantly higher than established percentiles at each week of gestation (p < .001). Only three pregnancies ended in fetal demise in the t21 population, two of which had persistently elevated Dopplers above the 95th percentile per established reference percentiles.

CONCLUSIONS

At each week of gestation, UA Doppler indices in t21 fetuses were significantly higher than established percentiles from a euploid population. Reference intervals based on euploid fetuses may therefore not be appropriate for antenatal surveillance of fetuses with t21. Prospective studies are needed to investigate the role and impact of serial UA Doppler velocimetry in the surveillance of pregnancies complicated by fetal t21.

Comparative study of umbilical cord cross-sectional area in foetuses with isolated single umbilical artery and normal umbilical artery

Single umbilical artery (SUA) is one of the most common prenatal diagnoses in cases of foetal abnormality. This prospective study evaluated 77 foetuses with isolated SUAs and 77 healthy foetuses, both at 22-39 gestational weeks. We categorised gestational age into the second and third trimesters, measured the umbilical arterial blood flow parameters and calculated the umbilical vein (UV) area, umbilical artery (UA) area and UV area/UA area ratio. In the second and third trimesters, a higher UA area was obtained in the isolated SUA group than in the control group (p < .01). Furthermore, the isolated SUA group had a lower UV area/UA area ratio than the control group (p < .01), and a positive linear correlation was found between gestational age and UV area in both groups (p < .01). The presence of isolated SUAs was associated with low birth weight and a high prevalence of small for gestational age.IMPACT STATEMENTWhat is already known on this subject? Single umbilical artery (SUA) is one of the most common prenatally diagnosed foetal abnormalities and approximately 80% foetuses with SUA have isolated SUA, which is a soft indicator of chromosome abnormalities, congenital malformations and premature birth. Umbilical cord cross-sectional area can be evaluated prenatally by ultrasound imaging. Normal values increase with gestational age and foetal size in single pregnancies. Changes in umbilical cord thickness have been associated with complications during pregnancy.What do the results of this study add? The correlation between gestational age and umbilical vein area in the isolated single umbilical artery (SUA) group and control group was better than that between gestational age and umbilical artery area. UA area increased significantly in both groups before 28 weeks but not after 28 weeks, particularly in the isolated SUA group.What are the implications of these findings for clinical practice and/or further research? The study provides a reliable basis for maternal foetal monitoring during pregnancy in the isolated SUA and control groups. Objective assessment of the occurrence and development of foetuses with isolated single umbilical artery was performed.

Isolated single umbilical artery and the risk of adverse perinatal outcome and third stage of labor complications: A population-based study

INTRODUCTION

Isolated single umbilical artery (iSUA) refers to single umbilical artery cords with no other fetal malformations. The association of iSUA to adverse outcome of pregnancy has not been consistently reported, and whether iSUA carries increased risk of third stage of labor complications has not been studied. We aimed to investigate the risk of adverse perinatal outcome, third stage of labor complications, and associated placental and cord characteristics in pregnancies with iSUA. A further aim was to assess the risk of recurrence of iSUA and anomalous cord or placenta characteristics in Norway.

MATERIAL AND METHODS

This was a population-based study of all singleton pregnancies with gestational age >16 weeks at birth using data from the Medical Birth Registry of Norway from 1999 to 2014 (n = 918 933). Odds ratios (OR) with 95% confidence intervals were calculated for adverse perinatal outcome (preterm birth, perinatal and intrauterine death, low Apgar score, transferral to neonatal intensive care ward, placental and cord characteristics [placental weight, cord length and knots, anomalous cord insertion, placental abruption and previa]), and third stage of labor complications (postpartum hemorrhage and the need for manual placental removal or curettage) in pregnancies with iSUA, and recurrence of iSUA using generalized estimating equations and logistic regression.

RESULTS

Pregnancies with iSUA carried increased risk of adverse perinatal outcome (OR 5.06, 95% confidence interval [CI] 4.26-6.02) and perinatal and intrauterine death (OR 5.62, 95% CI 4.69-6.73), and a 73% and 55% increased risk of preterm birth and small-for-gestational-age neonate, respectively. The presence of iSUA also carried increased risk of a small placenta, placenta previa and abruption, anomalous cord insertion, long cord, cord knot and third stage of labor complications. Women with iSUA, long cord or anomalous cord insertion in one pregnancy carried increased risk of iSUA in the subsequent pregnancy.

CONCLUSIONS

The presence of ISUA was associated with a more than five times increased risk of intrauterine and perinatal death and with placental and cord complications. The high associated risk of adverse outcome justifies follow up with assessment of fetal wellbeing in the third trimester, intrapartum surveillance and preparedness for third stage of labor complications.

Evaluation of right ventricular function in fetuses with isolated single umbilical artery using spatiotemporal image correlation M-mode

Background

Postnatal outcome of fetuses with isolated single umbilical artery (SUA) is determined mainly by right ventricular function. Our study examined whether there are differences in right ventricular function during the gestation period of fetuses with isolated SUA compared to healthy fetuses.

Methods

A prospective study was conducted on 77 fetuses with isolated SUA and 77 gestational age-matched controls from 22 to 39 weeks. For gestational age grouping, the isolated SUA fetuses and the control fetuses were divided into the second trimester group (22–27 weeks; 43 fetuses) and third trimester group (28–39 weeks; 34 fetuses). The fetal tricuspid annular plane systolic excursion (f-TAPSE) M-mode was applied to the tricuspid annulus, parallel to the ventricular septum, and the amplitude of the resulting wave was assessed using spatiotemporal image correlation (STIC) M-mode. We investigated the possible changes to the STIC M-mode indices during the course of pregnancy in both the isolated SUA and control groups. The relationship between f-TAPSE and gestational age was analyzed. Additionally, the correlations between f-TAPSE and birth weight was analyzed, and the birth weight differences between the isolated SUA and control groups in the third trimester were analyzed according to postpartum results.

Results

There was a significant difference in f-TAPSE between isolated SUA and control group in the third trimester (P < 0.05). There were significant correlations between gestational age (GA) and f-TAPSE among control fetuses (R² = 0.9049; P < 0.01). A significant, positive correlation between GA and f-TAPSE was also found with isolated SUA fetuses (R² = 0.8108; P < 0.01). The prevalence of small-for-gestational-age (SGA) fetuses and of discordant birth weight fetuses was significantly higher in the isolated SUA group than in the control group. In univariate analysis, the presence of an isolated SUA was associated with lower birth weight (2940 g compared with 3260 g) and with higher prevalence of SGA (13.0% compared with 3.9%; P < 0.01). The correlations between the birth weight and f-TAPSE in the two groups were analyzed in the third trimester, and the correlation in the isolated SUA group was better than that of the control group (R² was 0.623 and 0.463 in the isolated SUA group and the control group, respectively).

Conclusions

Right ventricular function in isolated SUA is altered as early as in fetal third trimester. STIC M-mode can measure the right heart function of the fetus and may predict isolated SUA with SGA.

Reference charts for umbilical Doppler pulsatility index in fetuses with isolated two-vessel cord

PURPOSE

To determine reference values for umbilical Doppler pulsatility index in fetuses with isolated two-vessel cord and to compare these values with standard umbilical Doppler pulsatility index curves from 23 to 40 gestational weeks.

METHODS

A retrospective longitudinal cohort study was conducted between January 2014 and December 2017 in a tertiary referral hospital and included 62 pregnant women with isolated single umbilical artery (two-vessel cord) and 174 measurements. Only uncomplicated term pregnancies were included. A reference curve for umbilical Doppler pulsatility index was built up and compared with a standard curve commonly used for fetuses with three-vessel cord.

RESULTS

Umbilical Doppler pulsatility index values were much lower than expected in cases with two-vessel cord compared to 3-vessel cord: mean of the regression equations was 1.02 ± 0.23 vs. 0.86 ± 0.19, respectively (p value < 0.001). This difference was quite constant across the gestational weeks considered, showing that the slopes of the two regressions were very similar.

CONCLUSION

Reference curves for umbilical Doppler pulsatility index in two-vessel cord pregnancies were determined. Pulsatility index values were significantly different compared with those commonly used for three-vessel cord. Using lower reference values for umbilical pulsatility index in cases with two-vessel cord may allow a better identification of fetuses affected with intrauterine growth restriction, thus improving fetal surveillance.

Quantitative Flow Imaging in Human Umbilical Vessels In Utero Using Nongated 2D Phase Contrast MRI

BACKGROUND

Volumetric assessment of afferent blood flow rate provides a measure of global organ perfusion. Phase-contrast magnetic resonance imaging (PCMRI) is a reliable tool for volumetric flow quantification, but given the challenges with motion and lack of physiologic gating signal, such studies, in vivo on the human placenta, are scant.

PURPOSE

To evaluate and apply a nongated (ng) PCMRI technique for quantifying blood flow rates in utero in umbilical vessels.

STUDY TYPE

Prospective study design.

STUDY POPULATION

Twenty-four pregnant women with median gestational age (GA) 30 4/7 weeks and interquartile range (IQR) 8 1/7 weeks.

FIELD STRENGTH/SEQUENCE

All scans were performed on a 3.0T Siemens Verio system using the ng-PCMRI technique.

ASSESSMENT

The GA-dependent increase in umbilical vein (UV) and arterial (UA) flow was compared to previously published values. Systematic error to be expected from ng-PCMRI, in the context of pulsatile UA flow and partial voluming, was studied through Monte-Carlo simulations, as a function of resolution and number of averages.

STATISTICAL TESTS

Correlation between the UA and UV was evaluated using a generalized linear model.

RESULTS

Simulations showed that ng-PCMRI measurement variance reduced by increasing the number of averages. For vessels on the order of 2 voxels in radius, partial voluming led to 10% underestimation in the flow. In fetuses, the average flow rates in UAs and UV were measured to be 203 ± 80 ml/min and 232 ± 92 ml/min and the normalized average flow rates were 140 ± 59 ml/min/kg and 155 ± 57 ml/min/kg, respectively. Excellent correlation was found between the total arterial flow vs. corresponding venous flow, with a slope of 1.08 (P = 0.036).

DATA CONCLUSION

Ng-PCMRI can provide accurate volumetric flow measurements in utero in the human umbilical vessels. Care needs to be taken to ensure sufficiently high-resolution data are acquired to minimize partial voluming-related errors.

LEVEL OF EVIDENCE

2 Technical Efficacy Stage 1 J. Magn. Reson. Imaging 2017.

Placental abnormalities associated with isolated single umbilical artery in small-for-gestational-age births

BACKGROUND

Previous studies have shown that pregnancies complicated by placentas with an isolated single umbilical artery (iSUA) are at increased risk for small-for-gestational-age (SGA) births. The etiology of SGA in this population, however, remains unknown.

OBJECTIVE

The primary objective of this study was to evaluate whether placental abnormalities in pregnancies with SGA births differ according to the presence of iSUA.

STUDY DESIGN

This was an observational study of all women with pathologic examination of the placenta after delivering a non-anomalous, singleton SGA neonate between January 2009 and August 2015. SGA was defined as birthweight less than 10th percentile for gestational age. Women were categorized according to whether they had an iSUA or a three-vessel cord. The following placental pathologies were compared between the groups using bivariable and multivariable analyses: SGA placenta, maternal vascular malperfusion, high grade fetal vascular malperfusion, and chronic villitis.

RESULTS

1833 women were included in the analysis: 34 with iSUA and 1799 with three-vessel cord. More than 85% of women in both groups had at least one placental abnormality. After adjusting for nulliparity and neonatal gender, the presence of iSUA was associated with increased odds of high grade fetal vascular malperfusion (adjusted odds ratio 2.8, 95% confidence interval 1.1-7.5) and decreased odds of maternal vascular malperfusion (adjusted odds ratio 0.2, 95% confidence interval 0.1-0.9). There was no significant association with other pathologic findings.

CONCLUSION

Pathologic placental findings associated with SGA birth differed based on umbilical cord composition. The presence of iSUA in an SGA birth was associated with a higher odds of high grade fetal vascular malperfusion abnormalities and lower odds of maternal vascular malperfusion abnormalities, compared to SGA birth with a 3VC.

Association of Isolated Single Umbilical Artery With Small for Gestational Age and Preterm Birth

OBJECTIVE

To assess the association of an isolated single umbilical artery with small for gestational age (SGA) and preterm birth.

METHODS

In this retrospective cohort study, 219 consecutive women carrying a fetus with an isolated single umbilical artery diagnosed during routine second-trimester anatomic survey were compared with 219 women carrying a fetus with a three-vessel cord. Pregnancies with fetal anomalies or aneuploidy were excluded from the analysis. Outcomes included pregnancy-induced hypertension, gestational age at birth, birth weight, SGA, defined as birth weight less than the 10th percentile, and indicated or spontaneous preterm birth, defined as delivery before 37 weeks of gestation.

RESULTS

In univariable analysis, the presence of an isolated single umbilical artery was significantly associated with lower birth weight (3,146 compared with 3,430 g) and with SGA (11.9% compared with 2.7%; P<.001 for each outcome). The rates of pregnancy-induced hypertension (7.3% compared with 1.8%, P=.01) and indicated but not spontaneous preterm delivery (5.5% compared with 0.9%, P=.01 for indicated and 8.2% compared with 4.6%, P=.12 for spontaneous) were also more common in pregnancies with an isolated single umbilical artery. In multivariable analysis controlling for potential confounders, an isolated single umbilical artery remained associated with SGA, pregnancy-induced hypertension, and medically indicated preterm birth (adjusted odds ratio [OR] 3.97, confidence interval [CI] 1.55-10.12; adjusted OR 3.50, CI 1.10-11.18; adjusted OR 7.35, CI 1.60-33.77, respectively).

CONCLUSION

Pregnancies complicated by isolated single umbilical artery are at increased risk for SGA and pregnancy-induced hypertension but not for spontaneous preterm birth.

LEVEL OF EVIDENCE

II.

Umbilical artery blood flows among pregnancies with single umbilical artery: a prospective case-control study

OBJECTIVES

To evaluate peak systolic velocity (PSV) in the umbilical artery (UA) among patients with single umbilical artery (SUA) as compared with patients with three vessel cords.

METHODS

A prospective case-control study was performed. UA blood flow velocimetry was obtained from fetuses with SUA and from a control group with three vessel cord. PSV and pulsatility index (PI) were measured. Patients' characteristics were compared for statistical differences and a linear regression model was constructed for the different groups.

RESULTS

UA Doppler velocimetry measurements were obtained from 29 patients with SUA and from 29 controls matched for gestational age. The differences between UA PI with and without SUA were significant (F = 3.471; p = 0.0379) showing a lower PI in the SUA group. However, no significant statistical difference was found in PSV between these two groups (F = 0.149; p = 0.86).

CONCLUSIONS

While the impedance in the UA of patients with a SUA was lower compared with patients with a normal umbilical cord, the PSV did not differ.

Perinatal outcome in cases of isolated single umbilical artery and its effects on neonatal cord blood gas indices

Abstract We aimed to evaluate perinatal outcomes and blood gas indices of isolated single umbilical artery (SUA). In this retrospective study, 134 fetuses with SUA were evaluated. A total of 77 (57.4%) fetuses with isolated SUA (iSUA) were compared with maternal age-matched 95 fetuses with double umbilical arteries (DUA), with respect to pregnancy outcome and umbilical cord blood gas indices. The incidence of SUA in our cohort was 1.04%. Patients with iSUA had lower neonatal birth weight compared with the control group (2,635 ± 972 g vs 2,991 ± 669 g; p = 0.009). Small for gestational age (SGA) frequency was higher in the group of iSUA when compared with fetuses with DUA (17.4% vs 5.4%; p = 0.03). Regarding the umbilical cord blood gas, the parameters were comparable between the two groups. SUA has a favourable obstetric outcome as long as the accompanying malformations are ruled out. Furthermore, neonatal cord blood gas parameters in fetuses with iSUA do not differ from fetuses with DUA.

The impact of isolated single umbilical artery on labor and delivery outcome

OBJECTIVE

Data regarding the association between isolated single umbilical artery (SUA) and pregnancy outcome are inconsistent and mainly address the risk of pregnancy complications. Thus, we aimed to focus on the association between isolated SUA, and labor and delivery.

METHODS

We conducted a case-control study of all singleton pregnancies diagnosed with isolated SUA (no known chromosomal/structural anomalies/fetal growth restriction) attempting vaginal delivery. Obstetric and neonatal outcome was compared with that of a control group of pregnancies with a three-vessel cord in a 1:2 ratio matched by parity. Composite adverse outcome included the following: Cesarean section (CS) and/or operative delivery due to non-reassuring fetal heart rate (NRFHR), prolonged neonatal admission, low Apgar score and umbilical artery pH < 7.2.

RESULTS

Out of 34 196 deliveries, 162 (0.5%) were diagnosed with SUA, and 91 (0.27%) were diagnosed with isolated SUA. Isolated SUA was associated with a higher rate of CS due to NRFHR (5.5% vs 1%, p = 0.02), small for gestational age (SGA) (14.3% vs 4.9%, p = 0.009), lower birth weight, and a higher rate of composite adverse outcome (20.9% vs 8.8%, p = 0.005). On multivariable analysis, isolated SUA was independently associated with an increased risk for composite adverse outcome (OR 2.34, 95% CI 1.05-5.21).

CONCLUSION

Isolated SUA is associated with increased risk for CS due to NRFHR and increased rate of SGA.

Long-term physical and neurologic development in newborn infants with isolated single umbilical artery

OBJECTIVE

This study compared birth parameters and the longitudinal course in physical and neurologic development between children with 2 and 3 vessel umbilical cords.

STUDY DESIGN

Our study of the Collaborative Perinatal Project included singletons of at least 24 weeks' gestation with single umbilical artery at birth and no identifiable congenital anomalies. Demographics that were collected included maternal age, race, smoking status, and socioeconomic index. Delivery data included gestational age, birthweight, Apgar scores, placental weight, and umbilical cord insertion and length. Growth and neurodevelopmental parameters were collected at various intervals from birth to 7 years.

RESULTS

There were 263 infants with isolated single umbilical artery and 41,415 infants with 3 vessel cords. A random effect model that controlled for potential confounders did not show clinically significant differences in the physical and neurodevelopment measures between these groups.

CONCLUSION

Our study shows no evidence of differential longitudinal physical growth or neurologic outcomes between infants with 2 or 3 vessel cords.

Middle cerebral artery blood flow velocimetry among healthy fetuses with a single umbilical artery

OBJECTIVE

A single umbilical artery (SUA) is an independent risk factor for perinatal morbidity and mortality in healthy fetuses. The aims of the study were (1) to determine middle cerebral artery (MCA) blood flow velocimetric values among fetuses without structural or chromosomal anomalies with an SUA and to compare them with nomograms of patients with a 3-vessel cord and (2) to measure the pulsatility index (PI) of the umbilical artery among these patients.

METHODS

The PI values of the MCA and umbilical arteries were determined prospectively among 98 healthy fetuses with an SUA. The PI values were compared with nomograms of patients with a 3-vessel umbilical cord. For the MCA, peak systolic velocity (PSV) was also measured. Patients carrying fetuses with intrauterine growth restriction or congenital anomalies were excluded from the study. Middle cerebral artery PI values below the fifth percentile and PSV values above the 95th percentile adjusted for gestational age were considered abnormal.

RESULTS

Gestational age ranged between 22 and 37.9 weeks (median, 30.3 weeks). After adjusting for gestational age, no alterations in the MCA PI and umbilical PI were found in comparison with the normal range for a 3-vessel cord known in the literature. Middle cerebral artery PSV values were also within the normal range for gestational age in all patients.

CONCLUSIONS

The MCA PI and PSV values among healthy fetuses with an isolated SUA were similar to nomograms for fetuses with a 3-vessel umbilical cord. Therefore, abnormal MCA PI and PSV values among fetuses with an SUA should be treated the same as in patients with a 3-vessel umbilical cord.

Antenatal detection of a single umbilical artery: does it matter?

The presence of a single umbilical artery is recognised as a soft marker for congenital anomalies, aneuploidy, earlier delivery and low birthweight. Most of the available data are derived from case series or highly selected populations and are therefore likely to be unrepresentative. In this retrospective case-comparison study, we firstly aimed to determine the incidence of a single umbilical artery in an unselected population and secondly to examine the clinical significance of this soft marker. Over a 40-month period, 107 cases were identified from a cohort of 35 066 births giving an incidence of 3.1 per 1000 total births and late pregnancy losses. The antenatal detection rate was only 30%. Compared to fetuses with normal cord vasculature, fetuses with a single umbilical artery were more likely to be delivered at an earlier gestation and to weigh less, were 1.7 times more likely to be delivered by a Caesarean section and 19% of the cases had a congenital anomaly. The perinatal mortality was 49.0 per 1000 total births, which was 6 times higher than the background hospital rate. The presence of a single umbilical artery is associated with a poorer perinatal outcome compared to that in fetuses with three vessels in the cord. Unfortunately, the antenatal detection rate is poor. Recognising the importance of this soft marker in counselling and management of pregnancies should provide the stimulus to improve detection rates.